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Volume 71, Issue 10
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MITSUYOSHI KIMATA1976 Volume 71 Issue 10 Pages 289-298
Published: October 05, 1976
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe albite synthesized from the gels of NaAISi3O8 composition in the system Na2O-Al203SiO2-H2O-CO2 has been investigated. The obliquity 2θ(131)-2θ(1_??_1) indicated that all the synthetic albites are of intermediate type according to the definition of albite polymorph given by Martin (1969). X-ray powder patterns for synthetic intermediate albite are reported for the first time. Some of synthetic albites are produced as single crystals, with which the intensity of reflection was measured by means of four-cricle diffractometer. The RF value; F1ko-F1_??_o/F1ko+F1_??_o proposed here seems convenient to characterize the structural state of albite polymorph. The IR spectra of these intermediate albites and its glass are reported in detail. In the DTA curve of high albite, an intersection. point 1116±7°C of the endothermic peak shows a striking similarity to the melting point, 1118±3°C, of albite suggested by Schairer and Bowen (1956). Polymozphism of the intermediate albite is discussed on the basis of the fact that some of natural and synthetic intermediate albites deviate from the linear trend between obliquity and their cell parameters.View full abstractDownload PDF (1123K) -
YUKIO TAKANO, YOSHIHIKO SHIMAZAKI1976 Volume 71 Issue 10 Pages 299-307
Published: October 05, 1976
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSFrom 67 non-translation space groups, the authors separated 6 space groups having two each pairs of diffraction patterns. Classification numbers of two figures were given to the total 73 non-translation space groups, so as to express their crystal system, elements of symmetry and lattice type. The rest 157 space groups, derived from these non-translation space groups, were provided with letters (four in maximum) to be put before or after the classification numbers of the basic space groups, to express their screw axis and glide plane. With this new style of notation, 157 space groups can be expressed by not more than three letters inclusive of the basic numerals. Thus, almost all space groups are represented by the symbols that are to to four letters fewer than those of the existing Hermann-Mauguin notation. This new notation enables even the beginners to identify the crystal system and the point group to which the space group belongs.View full abstractDownload PDF (523K) -
AKIRA ONO1976 Volume 71 Issue 10 Pages 308-322
Published: October 05, 1976
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSChemical analyses of garnet in pelitic rocks have been made by means of an electron probe microanalyzer. Special attention is drawn to give some clue to kinetics of garnet growth. Edges of an individual garnet crystal gave considerable chemical variation ranging from 0.5 to 2.0 wt% in MnO content. This is not due to garnet growth under disequilibrium condition but due to the fact that growth of garnet crystal took place at special edges and all parts of the crystal surface were not fomed at the same time. Near-equilibrium growth of garnet is revealed by the partition of Fe and Mg between biotite, cordierite and garnet.
Garnets in some thin section showed three kinds of zoning patterns: homogeneous, n ormal and reverse zoning patterns. Each garnet crystal showed different composition at both of center and edge of the crystal. Nucleii of garnet crystals did not start to grow at the same temperature, and cessation of garnet garnet growth occurred at different temperature for each garnet crystal.
Reversely zoned garnets which show increase of MnO content toward edge of the crystal are common in the investigated rocks. This type of zoning is never explained by the Mn-depletion model, and it is unlikely that all the reverse zonings were due to enrichment of Mn in pore fluid by supply of the element from unstalbe minerals. Probably, changes in temperature and pressure are one of the most important factors controlling zoning features of garnet.View full abstractDownload PDF (642K) -
SUSUMU NISHIMURA1976 Volume 71 Issue 10 Pages 323-326
Published: October 05, 1976
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe igneous rock specimens taken from Ikuno-Akenobe province in Japan were dated by the fission-track technique. Ages of pre-ore dikes, ranging from 72 to 65 my, are younger than ages of Ariga granite and Yakuno metamophic rocks in this province, which are 75 and 115 my, respectively. Being obvious from the ages of post-ore dikes, ranging from 55 to 51 my, none of the post-ore dikes in this province is younger than the Miocene time.View full abstractDownload PDF (114K)
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